1. Field of the Invention
The present invention relates to a transistor amplifier stage with an npn amplifier transistor of which the base is coupled to an alternating voltage input terminal, the emitter is coupled to a fixed potential and the collector is coupled to an alternating voltage output terminal. In particular, it relates to a radio-frequency (RF) transistor amplifier stage.
2. Description of the Prior Art
Various transistor amplifier stages are known which, however, for the most part have the disadvantage that when designed for high RF amplification their direct current stabilization is decreased. The Darlington stage is cited here as an example, wherein the emitter of a first transistor is connected with the base of a second transistor, and the collector of the second transistor is connected with the collector of the first transistor. In addition, in this known circuit the base of the first transistor is connected with the collector thereof via a first electrical resistance and is connected with ground via a second electrical resistance. Both the emitter of the first transistor and the emitter of the second transistor are connected with ground via a third or, respectively, a fourth electrical resistance. The base of the first transistor is coupled to an alternating voltage input terminal, and the collector of the second transistor is coupled to an alternating voltage output terminal. In order to achieve a sufficient RF amplification of the second transistor, the fourth resistor must be designed with a low value. However, in doing so, the direct current stabilization of the second transistor is correspondingly reduced.
An RF amplifier stage which includes, generally, a transistor having its base coupled to an alternating voltage input terminal, having its emitter coupled to a fixed potential, and having its collector coupled to an alternating voltage output terminal is known from Patent Abstracts of Japan, E-1366, May 18, 1993, vol. 17/no. 249 (JP-A-4 369 907). An integrated circuit for RF amplification on an MMIC chip, including a Darlington transistor arrangement, is specified in EP-A-0 544 387.